by Alison Young, USA TODAY

by Alison Young, USA TODAY

Scientists have found a "cocktail of synthetic stimulants" in a U.S.-made weight-loss supplement while investigating a series of health problems experienced by Dutch consumers, according to research published this week.

The supplements Dexaprine and Dexaprine XR are sold by California-based iForce Nutrition. Dexaprine XR continues to be sold in the USA through Internet sites, including Amazon.

Health officials in the Netherlands have issued alerts since last summer about Dexaprine products after consumers reported effects including nausea, agitation, palpitations and one cardiac arrest. But no such alerts have been issued to U.S. consumers.

Officials at iForce Nutrition did not respond to requests for interviews Friday. The company in 2011 pleaded guilty to manufacturing supplements that contained synthetic steroids, court records show.

Packages of Dexaprine list natural ingredients such as a type of shrub called acacia rigidula, citrus aurantium and green tea extract.

Yet the test results published this week by Dutch researchers show Dexaprine tablets taken by consumers who experienced increased heart rates, persistent vomiting, chest pain and other adverse health effects contained a variety of stimulants and other compounds. They included a synthetic amphetamine-like compound and deterenol, a compound briefly explored in pre-clinical drug development but never fully researched for its effects in humans.

"I think the point is that we can't be sure of what's really in these dietary supplements until we test them in the lab," said Bastiaan Venhuis of the National Institute for Public Health and the Environment in the Netherlands, whose team tested the Dexaprine supplements. Their results were published in the journal Drug Testing and Analysis.

"This important Dutch paper mirrors the other research out there, which has found high levels of synthetic designer amphetamine-like stimulants in many products," said Amy Eichner of the U.S. Anti-Doping Agency, which monitors athletes for performance-enhancing substances, including stimulants.

At least one U.S. consumer has reported suffering "life threatening" heart and other health effects that required hospitalization after taking Dexaprine and another supplement, according to adverse events data from 2012 obtained by USA TODAY under the Freedom of Information Act. The FDA didn't respond to questions Friday about whether it had received any more recent reports about Dexaprine products.

Pieter Cohen, an assistant professor at Harvard Medical School who studies supplements, said Dexaprine is the latest example of how the U.S. system of regulating the safety of these products is failing. He said it's unclear whether the Dexaprine formulas that sickened consumers in the Netherlands are being used in the USA, or whether our country's fractured system of monitoring adverse events from the products has missed people getting sick.

"We see that there are certain companies that have a record of reintroducing these dangerous products," Cohen said, noting the previous criminal case involving iForce Nutrition. "The question is what's being done to shut down these companies?"

Jennifer Corbett Dooren, a spokeswoman for the U.S. Food and Drug Administration, said late Friday: "Our international food partners notified FDA of the recall. We are unable to comment on the existence of an FDA investigation."

Consumers who suspect they've suffered an adverse event associated with a dietary supplement can report the incident to the FDA at: www.safetyreporting.hhs.gov